Continuous low-temperature dehydration



`uly 1950 H. L. SMITH, JR

CONTINUOUS Low TEMPERATURE DEEYDRATTON l2 Sheets-Sheet l Filed Aug. 1,1945 i vm July 11, 1950 H. 1 SMITH, JR

CONTINUOUS Low TEMPERATURE DEHYDRATION l2 Sheets-Sheet 2 Filed Aug. 1,1945 juy 2950* H. L. SMITH, JR 295%093 CONTINUOUS LOW TEMPERATUREDEHYDRATION Filed Aug. 1, -1945 12 Sheens--Sheefl 5 my M, 1950 H. L.swarm, JR 2,515,09

CONTINUOUS LOW TEMPERATURE DEI-IYDRATION Filed Aug. l, 1945 l2Sheets-Sheet 4 July ll, 1950 H. L.. SMITH, JR 2,55098 CONTINUOUS LOWTEMPERATURE DEHYDRATION Filed Aug. l, 1945 l2 Sheets-Sheet 5 July 1L1950 H. L.. sMm-n, .JR

CONTINUOUS LOW TEMPERATURE DEHYDRATION 12 Sheets-Sheet 6 Filed Aug. 1,19'45 mi mi fff/ July 1l, 1950 Filed Aug. 1, 1945 H. l.. SMITH, JR I2,515,098

CONTINUOUS LCIW TEMPERATURE DEHYDRATION l2 Shef'ets-Sheet 7 July 11,1950 H. L. SMITH, .-JR 2,515,098

CONTINUOUS LOW TEMPERATUE DEHYDRATION Filed Aug. 1, 1945 l2 Sheets-Sheet8l July 11, 195o H. n.. sMn-H, JR 2,515,098

CONTINUOUS LOW TEMPERATURE DEHYDRATION Filed Aug. l, 1945 12Sheets-Sheet 9 July M, 1950 H. L. SMITH, .JR 2,55,098

CONTINUOUS LOW TEMPERATURE DEHYDRATION Filed Aug. l, 1945 l2Sheets-Sheet lO July ll, 1950 H. l.. SMITH, JR

CONTINUOUS Low TEMPERATURE UEHYURATIUN 12 Sheetsheet 11 Filed Aug. l

h 1 v ,QW\ UU July 1l, 1950 H, L SMITH, JR 2,515,098

CONTINUOUS LOW TEMPERATURE DEHYDRATION Patented July' 11, 195oCONTINUOUS LOW-TEMPERATURE DEHYDRATION Horace L. Smith, Jr., Richmond,Va., assignor to Chain Belt Company, Milwaukee, Wis., a. corporation ofWisconsin Application August 1, 1945, Serial No. 608,106 12 Claims. (Cl.34-5) The present invention relates to the low-temperature continuousdehydration of liquid-containing materials` such as comestibles,inorganic hydrous oxides, sera, and similar materials.

The dehydration of solid and liquid substances containing water, undersuch conditions that a dry product results which is capable of quick andsubstantially complete solubility in water to produce a material havingmost, if not all, of the desirable properties of the original materials,has

challenged the ingenuity of experimenters and inventors for many years.While, generally speaking, the dehydration, or drying, of materialscontaining liquids associated therewith, has been practiced, in a moreor less empirical manner for many centuries, it was not until quiterecently that proper attention has been paid to the resulting dried ordehydrated product. Formerly, operators of drying equipment werecontented with the production of a material that would have merely goodkeeping qualities, and which, hence, could be preserved for considerableperiods of time. When it came, however, to the production of driedproducts which in their original condition contained relatively largeamounts of water, or other liquid, the resulting dried products oftenleft much to be desired. While they might be posse:sed of good generalkeeping qualities, yet they would differ radically in taste from theoriginal material, and would, in many instances, also be difcultlysoluble, so that the so-called reconstitution of the material bydissolving it in an appropriate amount of liquid, such as water, wouldbe difficult or even impossible. This was particularly true ofcomestibles, such as milk, eggs, fruit juices, dried coffee extracts,and similar food products, and in the case of sera or other biologicallyactive material, such as blood plasma, etc.

About forty years ago a slow and cumbersome process of avoiding thesedifficulties was proposed, comprising the freezing of the material thatit was intended to dry, and the direct sublimation of the ice thereinunder a vacuum high enough to permit the ice to sublime withoutconversion thereof into the liquid condition. It was also proposed toeffect the freezing of the material by subjecting it to such lowpressure conditions as to effect vaporization of some of the watertherein, whereby, as the result of the energy In more recent years, muchactivity has occurred in the large scale drying of blood plasma andother physiological material by this freezingdrying process. In someinstances refrigeration at low temperatures was employed first toquickfreeze the material, whereafter the ice therein was sublimed undera very high vacuum while supplying gentle heat to the frozen material.In each and every instance, however, the process was strictly a batchoperation; and in most instances was applied to generally very smallindividual quantities of the material, as in the drying of blood plasmain relatively small glass flasks, which then also served as the packagefor the dried material.

On the other hand, so-called vacuum drying has also found much favorduring the past fifty or sixty years. Mainly by reason ome impossibilityof commercially producing the required Very high vacuum, such vacuumdrying has been accomplished at temperatures Well above the freezingpoint of water, say at about 50 to 70 C. To vaporize water at thesetemperatures, however, did not require particularly hiegrd grees ofvacuum, and ordinary comm aly available vacuum pumps, coupled withsuitable condensers, sufced to condense the water vapor formed.

consumed in the vaporization of the water, the

temperature of the product would be reducedto the freezing point of itsconstituent water, where' after, by supplying the necessary heat energy,the resulting ice would be sublimed, and a dry product result.

When, however, employing very high vacuum conditions, the pumping of thehighly attenuated water vapor made commercial application of highvacuumdrying operations on a large scale unfeasible.

In accordance with the present invention, however, for the first timehas very rapid and large scale dehydration under very high vacuumconditions been made possible, so that commercial dehydrationofcommodities such as milk, coffee extracts, fruit juices, egg albumen,animal blood, etc., at temperatures below the freezing point of watermight be rapidly and economically effected. When operating under theteachings of the presently to be described invention, as when dryingfrom the frozen state, a vacuum on the order of notexceeding about 4000microns absolute pressure (4 mm. Hg column) ls employed. Under such lowpressure conditions, aqueous materials introduced into the evacuatedspace so rapidly lose water by vaporization thatthey are almostinstantaneously frozen, so that by the application of sufficient heatenergy the rest of 'the water therein can be rapidly vaporized withoutmelting the ice in the frozen material. As a consequence of this, thedried products obtained are of such a nature that they are fully andquickly soluble in water, and whewixed with 1 ing belt, the illustrationmatical;

an amount of water corresponding to that which they originallycontained, will reproduce a liquid product which is practicallyindistinguishable from the original undried material. This isparticularly true of whole milk, cream, colee extracts and someof thefruit juices. It is also true of blood plasma, sera, and biologicallyactive materials.

In accordance with the present invention it becomes possible for thefirst time to dehydrate such materials at great productive capacity, andat a cost-which compares favorably with even the simplevvacuum dryinghitherto employed.

Accordingly, it is one of the objects of the present invention toprovide a process and apparatus for the continuous large scalelow-temperature dehydration or drying of a large group of materials,such as food products, sera, plasma,

biologically active materials, extracts', and even certain inorganicmaterials which, unless careess and apparatus, it is described invconnection with twelve sheets of drawings, in which Fig. l is adiagrammatic representation, in the nature of a partially illustrativeflow sheet, disclosing the entire assembled apparatus and the processcarried on therein, and furnishes a key to the assembly of theinstrumentalities described in the other drawings;

Fig. 2 is a longitudinal vertical section of the discharge-end of theapparatus;

Fig. 3 is a similar section of the feed-end of the apparatus, the twofigures together constitut" ing a longitudinal vertical ,section of theentire portion of the apparatus in which the drying accomplished;

Figs. 4 and-5 respectively are top plan views, partiallyin section,corresponding to the appa ratus shown in Figs. 2 and 3;

Fig. 6 is an elevation of one side of the apparatus;

Fig. 7 is an elevational view of one end of the apparatus showing themeans for access thereto;

Fig. 8 is a vertical section along the lines 8 -8 of Fig.2; 4

Fig. 9, on a somewhat reduced scale, is a section along the line 9-9 ofFig. 2;

Fig. 10 is a side view of that portion of the .3 apparatus shown in Fig.3 by means of which the material to be dried is placed upon the drybeingpartly diagram- Fig. 11 is a side elevational view. on an enlargedscale.' of the means employed to remove dried material'from the dryingbelt;

Fig. 12 isv an end view, partially-in section, of the apparatus vshownlnFig.1l;

Fig. 13 is a side elevation, on an enlarged scale, of theinstrumentalities employed for removing dried material from theapparatus without destroying the vacuum conditions therein;

Fig. 1 6 is a vertical section along the line IS-IE of Fig. 1 5;

Fig. 17 is'a cross section along of Fig. 15; and

Fig. 18V is aside elevation, on a reduced scale,

the une 1 -I1 of an assembly of platens used to heat the drying belt.

` The process employed for carrying out the low temperature dehydrationcomprises in essence the application of a thin layer of a owablematerial containing the liquid which is to be removed, for examplewater, to a moving heat-conducting conveying means, which latter are`maintained in an evacuated' space maintained at a gas pressure of notover about 4 000 microns, that is to say, 4 millimeters absolutepressure (mercury column), thus substantially instantly freezing theapplied material upon and in contact with said conveying means as aresult of the loss of heat occasioned by the vrapidvaporizationtherefrom of some of its constituent water. Thereafter, and

while said conveying means are still in continuous motion, the materialfrozen thereon is dried by volume, no attempt is made to removethiswater vapor from the evacuated space, but on the contrary the watervapor is immediately condensed within the space by means of a'refrigerated liquid which at the temperature at which it is used has avapor tension so low as not to yield any vapor of its own to theevacuated space. This liquid may be either one in which the vapor issoluble,

such for example' as suitable brine, for instance lithiumv chloride orthe like, or may be some other suiiiciently cold liquid which is capableof condensing the water directly to ice, forming therewith a slush whichis still capable of being pumpl out of the apparatus into normalatmospheric pressure surroundings, whereupon thewater may be eitherevaporated from the brine, or'in case .of the use of a non-miscibleliquid, separated therefrom by gravity. It is another feature of theprocess to'refrigerate the cooling agent, and

then to reintroduce it into the apparatus, all as more fully disclosedand claimed herein below.

' its original concentrated condition, heat is required to vaporize.water Atherefrom with the resultant formation of steam, which steam isthen employed to heat the heating medium which serves to supply heatunits to the frozen material which is being dehydrated. i

Referring more particularly to Fig. 1, which is a flow sheet of theprocess, there is maintained within the evacuated space l, designated bydash and dot linesv in the central right hand portion or the figure, avacuum of not exceeding 4000 microns (4 millimeters Hg column).

While most of the elements shown in Fig. 1 are illustrateddiagrammatically by side elevations, certain of theelements in theevacuated.

or vacuum drying space I are shown, on the contrary, as a top plan view,in order that their functions may be more readily understood.

It is of course also to be understood that the' actual location of thevarious parts is not necessarily that shown in Fig. l, and therelationship of the parts will be more fully described in connectionwiththe other more detailed illustrations.

Referring primarily to Fig. 1, the evacuated or vacuum drying space Icontains a moving heatconducting conveying means 2 which is supported,and given a translational movement in the general direction of thearrow, (thatis, to the left),

by means of rollers 3 and 4, located at opposite ends of an archedsupporting or bridge-heatingplaten 5, upon which the conveying means 2slides. This conveying means 2 is preferably made of a suitable metalwhich willl not corrod'e or rust such as stainless steel, aluminum, orthe like, and therefore will not contaminate the material which is beingdried. The supporting and heating means 5 are preferably a plurality ofa separate adjacent platens. A suitable heating medium, for example,warm water, is caused to circulate through each of the heating means 5,being introduced, for example, by means of pipes 6, the flow of Water orother heating medium through each platen being indicated by means ofsuitable flow meters 1. The heating medium is caused to traverse theheating means 5. in a circuitous path as a result of internally thereoflocated baiiles 8, so that the heating medium will take approximatelythe course indicated by the broken arrows. The heating medium iswithdrawn through the pipes 9, and eventually finds its way throughpipes I into a collecting pipe II which leads to the heat exchanger I2,whosecoil I3 it traverses, eventually issuing therefrom through pipes I4and I5, whence it is conducted by pumps I6 to pipes I1 leading to theaforementioned i-low meters 1 and hence through pipes Ii to the heatingmeans 5. Suitable valves I8 are provided at the various parts of theapparatus so that the flow may be controlled, as under somecircumstances it is desirable to take some of the liquid heating mediumback from pipes I0 into pipes I1. Suitable pressure gauges I9 andthermometers 20 are provided so that the pressure and temperatureconditions existing in the platens may be known to and under the controlof the operator. These various vdevices will be described in greaterdetail in connection with the individual gures of the actual apparatusillustrated.

There are also present, although not illustrated on the now sheet, meanswhich deposit the material to be dried upon the conveying means 2, andthere are also further means such as a doctor blade (shown in detail inthe other views), which scrapes the dried material from the other end ofthe conveying means 2, and causes it to be deposited upon transverselythereof operating means |23 which serve to conduct the dry material tocollecting and packing means (not illustrated in Fig. 1, but which willbev described in detail hereinbelow). The actual vacuum pump which isemployed to create and maintain a vacuum in the space I is notillustrated in Fig. 1, as it consists of a well-known type ofinstrumentality whose exact point of connection is described in detailfurther on.

In order to condense the vapor produced as a result of the vaporizationof the moisture in the material which is dried on the conveying means 2,there are also provided a plurality of spray nozzles 2I which are purelydiagrammatically illustrated in Fig. 1, and which in actual practice arelocated directly beneath the conveyor 2. On the oor of the evacuated orvacuum drying space I there is a collecting tank so positioned that thecold absorbent sprayed into the chamber will tend to collect therein andflow to the sump 22 from whence it is conducted out of the apparatusfrom the pipe 23 by means of the sorbent pump 24, there being a suitablevalve 25 for the control of said flow. A suitable set of louvres 26,through which the evolved water vapor passes, is also provided. Thetemperature at which the condensing agent. sorbent or brine is sprayedinto the apparatus through the spray nozzl `which are fed by means ofthe pipe 21, is so that even under the conditions of low pressureexisting in the evacuated space I there is substantially no vaporliberated therefrom. In fact, any solvent vapor or water vapor which isbeing removed from the material that is undergoing the drying willeither be at once condensed into ice in case the sorbent is a non-watermlscible material or will be dissolved therein in case it is a brinesuch as a solution of lithium chloride. The exact strength of such brineand its further methodv of handling will be described furtherhereinbelow in connection with the description of the actual apparatus.

A thermometer 23 indicates the temperature of the sorbent which isflowing through pipe 21. The sorbent is refrigerated in the directexpansion sorbent-cooler 29 in which porbent is cooled by directexpansion of li ammonia which is contained in high pressureliquid-ammonia container 30, being expanded into the cooler through theexpansion-valve 3I located in pipe 32, which leads from the receiver 30to the sorbent-cooler 29. In ordinary operations the dilution of thesorbent which is sprayed into the evacuated space I from the nozzles 2|is rather gradual, and during the early part of the run of the apparatusit may not be necessary to fortify or strengthen the sorbent, such forexample as lithium chloride brine, until it has been so diluted bycondensed water vapor as to tend to give off vapor itself, whereafterits concentration is necessary.

Taking up the ilow of the sorbent or brine flowing out of the evacuatedspace I through the sump 22 and line 23, this, under the control ofvalve 25 and pump 24, is pumped through line 33, which is provided withgauge 34, through the flow meter 35, and through valve 36 and pipe 31,Into .the sorbent-cooler 29 which it traverses through a suitable coil(not shown), issuing through the pipe 21 to be returned to the spraynozzles 2l. There is, however, provided a branch pipe 33, and athermometer 39, the former leading to a heat exchanger 49 which consistsof a centrally located pipe 4I and a jacket 42. The sorbent liquid orbrine, which although at this stage is not as cold as it was whensprayed into .the space I, is still quite cool, and thereforeadvantageously may be partially heated before being envto the sorbentconcentrato;` 61 (see hereinbelow). In order not to confuse thedescription of the flow, suiice it to say for the moment that a portionof the sorbent entering the jacket 42 of the heat exchanger 40 flowstherethrough and leaves it through the pipe 43, and enters theheat-exchanging coil 44 of heat exchanger 45, thereby cooling the waterilowing therethrough and which water is introduced through the wate;-supply pipe |31 (see upper left-hand corner cf Fig. 1). Under thecontrol of flow meier 4-3, the water traverses the main body of the-heat excha `p45, and as a result of the cooled partially dilu e sorbentor brine passing through coil 44 therein, it is cooled, the thus cooledwater thence ilowing through pipe 41 into the ammonia condenser 48.Thermometer 49 enables the ascertainment of the temperature of the waterowing through pipe 41 inta ammonia condenser 48. In this ammoniacondenser there is introduced. through pipe 50, compressed anhydrcusammonia coming from the ammonia compressor 5I. This greatly compressesthe gaseous anhydrous ammonia so that under the inuence of the coldwater traversing the ammonia condenser 48 the ammonia is condensed intothe liquid state, and thence is transferred by pipe 52 into theliquid-ammonia receiver 30, where it is stored until expanded throughvalve 3l back into the sorbent-cooler 29, wherein the liquid ammoniavaporizes and is transformed into the vapor state, the resultant coolingeffect serving to refrigerate the sorbent or brine which is traversingthe sorbent-cooler 2s in indirect heatexchange relationship with thevaporizing ammonia. The resulting dry ammonia vapor leaves the sorbentcooler 29 through pipe 43, which conducts it back to the ammoniacompressor 5 I. -This therefore completes the ammonia cycle whichfurnishes the refrigeration required for the operation of the process.The water ilnally leaves the ammonia condenser 48 through the line 53which leads to the drain. A thermometer 54 is Provided so that thetemperature of this water may be ascertained.

Taking up the further flow of the sorbent which has become diluted as -aresult of the absorption of the water, for instance the lithium chloridebrine, and which has been mentioned as traversing the coil 44 of heatexchanger 45 (see upper left portion of Fig. l), the brine which has nowabsorbed some of the heat from the water owing through the heatexchanger 45 leaves the coil 44 through pipe 55, and enters a secondheat exchanger 56 flowing through the central pipe 51 thereof, andcontinues its ow through pipe 50, i ilow meter 59, pipe 60, and checkvalve 6I, thence flowing through automatically controlled valve 62 tothe gear pump 63, leaving this pump through pipe 64 and passing throughvariable flow control needle valve 65, and thence through pipe 66 intothe sorbent concentrator 61, which consists of a suitable boiler ortank, in which the sorbent or brine may be heated by means of the burner60 whichis under the control of the modulating sorbent concentrator 61..The reason for controlling the gas valve also at this point is toprevent heating of the boiler when the level is lower than thatpredetermined. There is thus a burner control both by the level of thematerial -as well as by the temperature of the vapor space thereof.There is also a thermometer 11 which enables the temperature to bedetermined in the concentrator 51. Other safety valves and gauges areprovided, as indicated.

'I'he switch 19 -actuated by lever 18 is so arranged that when the levelof the sorbent in the concentrator falls, the switch will be closed soas to drive motor 80. deriving its energy from the main 8l, said motorbeing associated with the gear pump 63, so as to pump dilute brine orsorbent into the concentrator 61.

As the brine is concentrated through evaporation of water in the boiler,its boiling point increases. A thermostat 82 located within the brine isset for a temperature corresponding to the boiling point of the desiredconcentration of the brine at the pressure prevailing. When theconcentration of the brine reaches this amount, the thermostat 82energizes the solenoid valve 83 centrated brine from the line 04 to theline 05 leading to the heat exchanger coil 06 within the alreadymentioned heat exchanger 45, which is traversed by the cool waterflowing to the ammonia condenser 48. This hot concentrated brine is thuspartly cooled by the fresh water owing through valve 45 and meter 46 andthe thereby somewhat cooled concentrated brine is then passed throughpipe 01 and flow meter 08 into the interior pipe 4I of the alreadyherein-above described heat exchanger 42, leaving the latter throughline which directs it through valve 9| into pipe 23 where it joins theow of the cooled concentrated brine flowing from the sump 22. By meansof lheat exchange effected by the instrumentalities just recited thereis but little loss of heat, and the residual refrigerative eiect of thepartially diluted sorbent or brine is fully utilized and transferred tothe water which serves to cool the compressed ammonia gas so as tocondense it back into liquid ammonia in the ammonia condenser` 48.

When the sorbent or brine is concentrated in concentrator 61 there willof course be developed a certain amount of steam, which leaves the topof the concentrator 61 through the pipe 92 passing through the pipe 93and a spray trap 94 and thence through the line 95 into the jacket ofthe heat exchanger or hot water heater I2 serving to heat the watertherein. Hot condensate leaves the heat exchanger or water-heater I2through the line 96 and passes through the jacket 91 of heat exchanger56 and eventually leaves the system through discharge pipe 98. Itsresidual heat is thus transferred to the partially spent sorbent orbrine which has already absorbed some of the heat from the water supplyin heat exchanger 45. There again eilicient heat exchange and saving ofheat units is effected.

If the steam demand for heating the platens is in excess of thatsupplied by the necessary regeneration of the brine, a connection |03with the city water supply I31 controlled by the valve I04 permitsmake-upto the desired amount.

Additional thermometers and gauges are shown at various points, but astheir -function is selfevident it is not deemed necessary to describeeach one of them in detail. Moreover, there is also provided anexpansion tank I05 which is connected through line II to the alreadymentioned hot water heater I2. In line 95 (see lower left-hand corner ofFig. 1) there is a valve |06 which is normally open so that steam mayflow to the hot water heater I2. It is, however. under the control of athermostatic control I 01 which serves to throttle the flow of steam incase the out-going water from the water heater, and which flows throughline I5 to the pumps I6, gets too hot. Thermometer |08 serves toindicate the temperature of this water and is connected to the line I4.In other words, if the water gets too hot, steam valve |06 is throttleddown ork causing it to open and permitting passage of con- 75 separatesections which are supported upon 9 suitable beams |09. It isconveniently termed a bridge as it is upwardly arched and the belttravels across it.

It will be noticed that each of the sections is subdivided into a numberof individual parts by the partitions 8, which extend only partiallyacross, as can best be seen from the diagrammatic illustration in Fig.1, and also in Figs. l5, 16 and 17, thus providing a circuitous path forthe heating liquid.

The belt 2, which moves to the left as shown by the arrows in bothsFigs. 2 and 3, vfinally passes over the roller 4 (left side of Fig. 2),and returns to roller 3, means being provided in the form of the rollerH which is supported on lever H I which in turn is pinioned on thebearing H2, there being tensioning means attached to the frame work andbearing the broad reference numeral I3. This is a more or 1ess commontype of tensioning device to insure the tightness of the belt and anadjustment may be made by means of the screw H4. A suitable motor H5(Fig. 2) shown as being contained within the housing serves by means ofchain-belt H6 and pulley H1 to impart movement to the roller 4, whichserves to pull the belt in the direction shown.

At a short distance above the belt 2 and as shown in the upperright-hand corner of Fig. 3 there is shown the pipe H8 which feeds spraynozzles H9, which serve to distribute the material that is to bedehydrated upon the belt 2. The material is applied in liquid formthrough the pipe H8 under suilicient pressure so that, upon leaving theorifices of the spray-heads ||9, it willbreak into a very ne mist, whichhas sufficient momentum to bring it into contact with the belt 2. Theforce with which the material is applied is such that despite the factthat evaporation from the droplets takes place almost instantaneously byreason of the low pressure (high vacuum) existing in the apparatus, thematerial will still be liquid at the time that it contacts with the belt2, as a result of which the small individual spherical droplets ofmaterial will tend to flatten themselves against the belt 2. Thisparticular feature is illustrated in greater detail in connection withFig. l0. By reason of the rapid vaporization of the Water from thematerial, it will soon attain a temperature well below the freezingpoint of water, i. e. below 0 C. (32 F,) so that after the belt hasprogressed but a short distance to the left, the material will be foundto have frozen thereon in a thin but fairly uniform lm, As alreadymentioned, a

heating medium such as warm Water is passed through the various sectionsof the arched bridge platen 5, and the various sections thereof may beheated to different temperatures, if desired; for instance the centralsection may be heated to a higher temperature than either of the sides,or under some circumstances, where the product is not tooheat-sensitive, the last plate, that is the one furthest to the left inFig. 2, may be at a higher temperature than the other two sections.

The progress of the material through the machine can be observed throughthe numerous windows |20 which are provided along both' sides of thechamber As the material becomes dehydrated in accordance with thegeneral description already given, and arrives at the point of the beltwhich is on roller 4 (left upper side of Fig. 2), the material will tendto fall off the belt 2 asitmakes a turn around roller 4, but to insurethe complete removal of the material there is provided the resilientlymounted doctor-blade |2| which causes the dried material to fall in theform of a flaky powder into the hopper |22 located immediately below theroller 4, and the doctor-blade |2|. The mechanism for operating thisdoctor-blade is separately illustrated and described in connection withFigs. 1l and l2. The material eventually falls on to a transverselythereof operating conveyor belt |23, which serves to convey the materialinto a set of hoppers on each side of the chamber, these hoppers servingto conduct the material through tubes |45 into packing devices broadlydesignated by the numeral |25, the construction of which is described indetail in connection with Figs. 13 and 14.

These receiving or packing devices |25 are intended to be operatedalternately, and for that reason the belt |23 is alternately movedeither in a direction away from or toward the beholder (as viewed inFig. 2), movement being .imparted to the belt by means of the motor |26which, by means of the chain belt |21, drives the shaft |28. Theoperation of motor |26 is under the control of the operator from a pointoutside of chamber The upwardly arched plates of the bridge platen 5 aregenerally supported within the apparatus by means of longitudinal beams|29 and cross-beams |09.

The condensing means for the Water vapor which evolves from the materialwhich is traversing the chamber on belt 2 consists of the following:

The heavily insulated tank generally designated by the reference numeral|30 consists of two metallic walls between which there is an insulating4packing |3|. Into this gener Areceiving vessel or tank |30 there is`spyslthrough spray nozzles 2|, fed by pipe 21 a refrigerated sorbent orcooling medium, for example lithium chloride brine which may for exampleconsist of a 10 molal solution of lithium chloride. As will be seen fromFigs. 2 and 3, these spray nozzles 2| and pipe 21 are located below thebelt 2 and its supporting structure. In order to avoid any of the sprayfrom getting on to the belt and thereby possibly contaminating theproduct, there are provided the horizontally disposed series of louvers|32, through which the Water vapor evolved from the material undergoingdrying may freely pass, so as to become absorbed in the spray orsorbent, or condenseddjrectly to ice thereby. The sorbent materialcollbts in the bottom of the tank |30, and nally leaves through the sump22 which is at about the center of the chamber I and is shown in theextreme lower right of Fig. 2.

Pipe 23 and valve 25 control the flow of brine or other sorbent fromchamber By reason of the high vacuum existing therein, punlp 24 (whichwas shown in Fig. 1) is used to effect the flow of the sprayed andre-collected brine.

The means for attaining the desiredvacuum consists of a vacuum pump |33which is connected with the chamber by means of the pipe |34 which issomewhat broadened into the form of a funnel |35 within the portion 20|of the chamber which closely adjoins the aforementioned collectinghopper |22.

In order to prevent any of the brine or sorbent vspray from being drawninto the vacuum pump, there are provided the vertical and slantinglouvers 99,'.and the entrainment-eliminators |36.

The louvers 99 and their supporting plate 202,

and the louvers |36 serve to form chambers 20| and 203 which are boundedat the top by the imperforate'plate 200, so that all of the gases andvapors evolved from the material that is being dried on the belt 2 musttraverse the spray ofcooling and condensing agent or sorbent sprayedfrom nozzles 2|', whereby any condensible water or other vapor will becondensed and/or absorbed by said cooling agent or sorbent.

The residual gases hence must find their wayv about 4000 microns (4millimeters Hg column) The chamber is rendered accessible to entry, whennot in use, by means of the suspended door |40 (see Figs. 5, 6 and '7),and the entire chamber is supportedupon pillars |4| on. the floor |42.Fig. 6 shows the pumps' I6,v the flow-meters 1, pipes 6, 9 and I8, andthe various gauges and thermometers I9 and 20, already described inconnection with Fig. 1. The pumps are mounted I on suitableV concretefoundations |43, and the door |40 is supported by the support |44 sothat, if necessary, it can be entirely swung aside lto permit portionsof the interior fittings of the apparatus to be moved in and out, or tobe ad- .iusted if desired.

By` means of the flow-meters 1, and the various thermometers, gauges andcontrol mechanism, which, advantageously all can be concentrated on asingle control panel in full view-of the operator, the operation of theapparatus, and the raccurate control of the process, can be carried out.By reason of the excellent correlation of heatinput andvheat-consumption, the operation of the process is practically asinexpensive as the more or less common type of vacuum drying systemshitherto employed, with the .added advantage that the products obtainedare readily reconstituted to the original condition bythe mere additionof the appropriate amounts. of water, corresponding to that present inthe original product.

After the apparatus has been described in more minute detail, examplesof the actual dehydration of a number of products will be given.

As already briefly indicated, means are pro-r vided for removing driedmaterial from the chamber without interfering lwith the continuouscarrying out of the operations therein conducted, and withouteifectivelyvarying thehigh vacuum conditions therein existing. Thus material thatis being scraped from the main drying-belt 2 by means of the ,adjustabledoctorblade |2| (whose precise construction' will be taken uphereinbelow), falls through'the funnel |22 onto the transverse carryingbelt |23, which In detail (see Figs. 13 and 14), these lling deviceseach consist of a chamber |46 which is suitably supported from thechamber by means of I- or T-beams |41 and is in direct communicationwith the chamber through the passageway |48 through which the tube |45also passes. The passageway and tube are, moreover, capable of beingeffectively shut off from communication with the main chamber'l by meansof the sliding closure |49 which is capable of reciprocal movement,being actuated by meansv of the rack |50 and pinion |5I, the latterbeingmounted upon shaft |52, the latter being provided with a hand-wheel|53. When the shaft |52 is rotated in a clockwise direction- (Fig. 14),the closure |49 will be drawn to the right, so that any material `lowingthrough lthe chute |45 may flow into a bottle or jar l|54 which issupported in a glass housing |55 within a supporting member |56, whichlatter may be given an upward or downward movement through theintermediation of the screw |51 which is operated by means of the rod|58 which is provided with the handwheel |59. The glass housing |55 issecured to the chamber |46 by means of four vertically extending rods|60 which support the cylindrical glass housing |55 by means of theplatform |6| through which the screws |51 and shaft |53 pass, the 'rodsbeing passed through ears |62 and secured by wing-nuts |63. Suitablegaskets |64 and |64' serve to provide air-tight seals between the glasshousing 55 and the platform |6|. To provide for larger containers thanthe may be of metal, rubber, canvas, etc., and which v devices broadlydesignated as |25. j

jars |54, a larger housing and therewith associated rods of the sametype as rods |60 may be provided, as indicated in dotted lines in Fig.13. The principle of operation, however, is theA same.r

In case it isv desired to seal the dried material either in vacuo or inan inert gas, the following conveniences are provided. Anelectromagnetic holder |10 provided with a solenoid |1| and leadwires|12 (which are connected to a source ofv direct current-such as abattery, not shown) is attached to the closure-member |49 so as to bemovable therewith. A suitable cap (not shown) may be magnetically heldvto the closure-member when the latter is in the position shown in Fig.14. Then, when the jar is in place and a suitably high vacuum has beenproduced in the space |46 by exhausting'theair therefrom, as for exampleby means of the pipe |15, the closure member may be moved to the rightby means of the rack |50 and pinion- |51, thereby carrying Vthe cap lisadmitted into the space |46 the cap will be firmly` pressed against ltheperiphery of the jar j by the outer pressure; while a vacuum will bemaintained within the jar. lIn Athe latter case.

lthe vacuumc'ould be broken with ordinary air.

However, anjinertgas is preferred. When putting a newvjar in place, thespace |46 must be evacuated tol the same degree voi? vacuum so that Or,the

be substantially altered, as this might interfere with the properoperation of the drying process being performed therein.

In order to insure a tight sealing off ofthe chamber I from the space|46, gaskets 263 and 264 are provided. The manner of attachment of thehousing |14, which provides the space |46, to the main body of theapparatus will be selfevident from the construction shown in Figs. 13and 14. The housing |14 is provided with a suitable plate |16 which issuitably bolted to the end of said housing by means of the bolts |16'.In order to provide for smooth operation of the closure member |49, itis provided with a slidingframe |11 which rides on rollers |18.

The closure member |49 is constructed of two main parts. The upper part220 may be moved vertically so as to make tight contact with the gasket263. This is accomplished by providing the two rollers 22| which pinionon said upper part. The lower part 222, which is separate from the upperpart 220, has an inclined surface upon which said rollers 22| may roll.With the device shown in the position illustrated in Fig 14, the lowerpart has traveled to the eXtreme left and has in consequence thereofraised the upper part of the device against the gasket 263. The spring|19 tends slightly to push the device to the right. When the gear wheelis turned clockwise, the first effect will be to draw the portion 222 tothe right, as a result of which the part 220 will drop f away from thegasket 263. Shortly thereafter, the entire device |49 will also move tothe right so that eventually there will be no obstruction between thechute |45 and the jar |54, so that material can freely flow into it. Onreversing the operation, the closure |49 will first ride to the leftuntil it is in alignment with the opening of chute |45, whereafter as aresult of the further leftward movement, of the portion 222 the upperpart will rise upwardly until it is pressed into engagement with thegasket 263. When, thereafter, air or gas is admitted into space'l46, thepressure of the part 220 against the gasket 263 will ensure a tightseal.

The entire assembly |25 (see Figs. 9, 13 and 14) thus serves as a meansfor removing material from the apparatus during its operation withoutdisturbing the vacuum and other conditions therein; and the entireassembly forms a single element of some of the subjoined claims.

Fig. 10 is a diagrammatic representation, on an enlarged scale, of theaction of the spray nozzles and what happens when they deposit thematerial which is to be dehydrated upon the belt 2. It will be noticedthat the particles issuing from the nozzle, and which approach the belt,are shown as vcomposed of substantially spherical droplets which,however, become flattened out as they hit the belt. An attempt has beenmade to indicate their frozen condition by shading the flatteneddroplets at the point immediately below the arrow which indicates thedirection of movement of the belt to the left. By reason of the factthat the particles or globules while in transit toward the belt presenta minimum of surface, the area from which vaporization can take place isdefinitely restricted so that even though evaporation of llquid or waterfrom the droplets begins instantaneously when they get into the lowpressure surroundings, there would be insufficient vaporization to causethem to be come ice particles, which, if it did occur, would cause themto bounce away from the belt 2 instead of being deposited thereon.

An important feature of the present invention resides in coordinating,for a given product, the pressure on the product as it enters the spraynozzles in conjunction with the size of the nozzle orifice so that thesize of the droplets produced and their velocity may be controlled,whereby freezing of the particles is delayed until they strike the belt.When they hit the belt, the particles are flattened against the same,thereby blending to form a more or less continuous lm. The increase inthe surface area of the mrticles after they are flattened against thebelfpermits liberation of water vapor from within the droplets, theinternal pressure being sufficient to overcome the surface tension, andrapid freezing then occurs. The quantity of material sprayed into thechamber and the speed of the belt determine the thickness of the filmdeposited on the belt.

The details relative to the operation of the doctor-blade |2| whichserves to remove the dried material from the belt 2, are illustrated inFigs. 11 and 12, which are on a somewhat larger scale than either Figs.l or 2.

By reason of the fact that the material which is dried on the belt 2,and which it is desired to remove shortly after the belt makes its turnaround the pulley 4, is a very thin layer, and as it is undesirable tobuild up a thick layer, and moreover as the belt should be reasonablyclear at the time the material is freshly sprayed thereonto, efficientmeans are provided for removing Substantially all of the material fromthe belt. For this reason the doctor-blade |2| is provided, which bearsagainst the belt 2 at a point where the belt is in contact with theroller 4.

The doctor-blade itself consists of main body |2| and the actual knife|80. Twife itself is bolted to the angle iron |8| whlch,is provided onthe shaft |82. Keyed to the said shaft is the lever |83 whose smallerend |84 is plvoted on the pivot |85, which latter is connected by meansof the rod |86 to the connecting member |81, the other end of which isconnected to the toggle |88 which pivots about the pin |89.

Intimately fastened to the toggle |88 is the handle |90. By reason ofthe link construction |9| provided with the slot |92 and by lifting thelever |90 upwardly and swinging it to the left, the connecting member|81 and the thereto connected rod |86 will be moved downwardly and tothe right so as to impart to shaft |82 a counterclockwise movement whichtherefore will move the angle iron |8| to which the doctor-blade |2| isattached in such a manner as to disengage the blade |80 of thedoctor-blade |2| from contact with the belt. Moreover, a suitable spring(not shown in the drawing) and which is contained within the housing |81of the connecting member and under the control of the threaded annularmember |93, is capable of accurately adjusting the pressure of thecontact of the blade |80 against the belt 2. The shaft |82 moreover isjournalled in plates |94, which plates are held to the side walls of theframe by means of the bolts which operate in slots |96 and |91, wherebythe exact position of the doctor-blade relative to the belt 2 and thepulley 4 can be adjusted. It is thus possible when necessary to alterthe angle of attack of the doctor-blade against the belt.

Whenever it is necessary to obtain access to the interior of the chamberI, the lady mentioned door |40 is provided, this bei uspended from thecrane |44 (see Fig. '7) which is capable of holding the weight of thedoor when the same is swung to one side. The door is fastened to thetight seal with the chamber I.

l5 end of the chamber I by means of a plurality of clamps 2I0 and which,after the door has been swung into the opening, are secured to the cham-I ber by means of bolts 2I2, said clamps bearing with their one endagainst the upstanding flanges 2li and with the other against the anges2I8 (which construction can best be seen at the extreme right side ofFig. 5). A suitable gasket 2 I3 is also provided so that the door willmake an air- Self-evidently as soon as the pressure in the chamber dropsas a result of pumping the air therefrom, the external air pressurebearing against the door H will force the same ever tighter against thegasket 2| 3 so that leakage will be practically prevented. It is,however, advisable to tighten up the nuts 2I3a .on bolts 2|! after thevacuum is established. If at any time the apparatus requires entry, thenuts 2I3a should preferably be somewhat loosened before air is admittedinto the apparatus, as otherwise they would bind so tightly as to bedifficult to open.

In order to permit accurate adjustment of the door MII into its opening,there is also a hangingbolt 2N which is attached to the door byconnection 2I5. 'I'he bolt carries a spring 2I5a strong enough tosupportl the load of the door but still permitting a limited amount ofmovement thereof in an upward and downward direction.

In Figs. 15, 16 and 17 are shown some of the details of the platenwhich, as already mentioned, is provided with the internal bailies 8which cause the liquid in the platens to take a circuitous path. Thepoint of entry and exit of the liquid is shown respectively at thethreaded openings ZIB into which pipe 6 leads, and theexit pipe 9, whichare threaded into the outlet ZIB.

Fig. 18 is purely illustrative of the general shape of the platen,which, as already has been mentioned, is upwardly convex for the purposeof insuring good heat-conducting contact with the belt 2.

'I'he operation of the apparatus will, it is believed, be evident fromthe description, particularly in connection with what has been saidregarding Fig. l. It is dimcult to give precise instructions as to thevarious temperatures, operational speed, etc., which may be employed, asthis of course depends a great deal upon the material which is beingsprayed into the apparatus.

As an example of the actual operation of the apparatus and to give someindications of its size, the following data are given:

The belt 2 is 2 wide, but its effective width is only 2li/2", as thespray nozzles IIS produce a width of sprayed material only 21 1,5 wide.In the drying of ordinary whole milk, the speed of the belt was l0 feetper minute, and inasmuch as in the machine in question the arched bridgeplaten 5 was 12 feet long, the period of contact between the belt 2 andthe platen 5 was, at the given belt speed, 1.2 minutes. The nozzles IISwere spaced a distance of. 6 inches from the belt and only 2 nozzleswere used at the time, being 5 inches apart, thus producing aconsiderable overlap. The nozzles actually used were known as of thehollow cone type furnished by the Spraying Systems Company, Chicago,Size No. 2.

The actual vacuum maintained in the chamber I was 500 microns and theplaten temperature was maintained uniformly at 200 F. The sorbent usedwas lithium chloride brine of about molal concentration, which in thecase of milk is high enough, and this brine had been refrigerated tosuch a temperature that at the time it 16 was sprayed into the apparatusto absorb the moisture given off by the drying milk it had a temperatureof 5 F. The temperature of the milk sprayed into the apparatus was 60 F.

In producing dried coffee extract, a Well roasted coffee was brewed withsuch quantities of water that the liquid coffee treated had aconcentration of from about 4 to 7%. The rate of feed in the case of theconcentrated coffee as well as in the case of milk was 1.6 gallons perhour for each nozzle or a total of 3.2 gallons per hour. The pressure onthe liquid entering the :nozzle was 10 pounds, the pressure drop acrossthe oriiice being of the order of 25 pounds due to the vacuum in thechamber.

The moisture content of the dried milk or dried coffee, whichever isbeing dried, was found to be about the same, namely about 1% residualmoisture.

It will of course be evident that many modifications may be made withinthe skill of the engineer in the precise construction of theinstrumentalities herein described, and moreover that the type of vacuumequipment used may be suitably varied as of course much of this isstandard commercial construction.

All of the essential features of the apparatus, such as has beenactually constructed and operated, have been fully described so that itsreproduction on the basis of this description will be possible on the`part of any properly skilled engineer.

The detailed description of the apparatus and of the process is more forthe purpose of teaching the art of the invention which is claimedherein, rather than to serve as a set of drawings or blueprints, andtherefore applicant does not desire to be limited to the precise detailsshown, but wishes his claims to be interpreted in the broadest aspectscommensurate with the prior art. Thus I the strength of the brine usedto absorb the water may be from about 6 molal upwards, if lithiumchloride is employed.

The essential feature in the present invention resides in theconstruction of the apparatus and the orientation of its various partsin such a manner as to make possible for the rst time large scalecontinuous commerical drying, from the frozen state, of aqueous productsin a continuous manner, as contrasted with the small scale individualbatch operations of the prior art, and of course also in the method ofeffecting such drying.

The present application is a continuation-inpart of applicants earlierfiled application Serial No. 515,844, filed December 27, 1943, nowabandoned..

Accordingly applicant claims:

1. A continuous process of dehydrating a iiowable aqueous material whichcomprises applying it in the form of a thin adherent layer to a movingheat-conducting conveying means positioned in an evacuated completelyclosed vessel maintained at a total gas pressureof not over about 4000microns, thus substantially instantly freezing the applied material uponsaid conveying means by loss of heat occasioned by the rapidvaporization therefrom of some of its constituent water, supplying heatto said conveying means and the material frozen thereonto to eiect theevaporation of the residual but now frozen water therein, whereby thematerial on the conveying means is dehydrated, within the same evacuatedvessel and in close proximity to said conveying means condensing theliberated water vapor by

